AR15.Com

Certainly a large gun forum, but quality is rather low. Admins seemed only concerned with generating large post counts to impress potential advertisers and not at all concerned with the quality of the forums.

Probably more than a few dead people with active user accounts.

I spent hours reading this website when I was a new AR-15 owner. I admit it was helpful, but there is a lot of chaff to wade through before you get to the wheat. Many topics end up being "pissing contests" between self proclaimed experts. It is also saturated with armchair commandoes who are convinced that the apocalypse is going to be tomorrow and can not wait to use their " safe queens".
That being said: If you are willing to put up with that, there are knowledgeable members who know these rifles well and share their expertise willingly.

Excellent site to learn how to build, customize, and accessorize an AR-15 style rifle or pistol. I've learned a lot about the AR platform on this site.

This administrators of this website blocked me from using their website, simply because I was trying to make contact with a member who supposedly sold me something, but then ended up going MIA. When I posted on his thread that I was having no luck communicating with him, and warned other members about he was not communicating with me, the site administrator blocked me and will not let me back onto the site.